This invention relates to expansion-joint belts used for sealing between last stages of steam turbines and inlets of condensers for steam-turbine power plants.
A steam turbine power plant often includes a condenser 10 (see FIG. 1) downstream of a last stage 14 of a steam turbine for condensing steam used in the steam turbine. A hood 12 is often attached to the last stage 14 (or a wall attached to the last stage) by an expansion-joint system 16 which includes a resilient belt 18 (although some prior-art belts are also of stainless steel) clamped to the last stage 14 of the steam turbine and the hood 12 of the condenser 10 by a last stage belt clamping mechanism 20 and a condenser belt clamping mechanism 22. A purpose of the resilient belt 18 is to allow relative movement (lateral and longitudinal and axial) between the last stage 14 of the turbine and the hood 12 of the condenser 10, while maintaining a vacuum (which often causes a pressure differential of as much as 15 psi) created in the hood 12 by the condenser 10. Such an expansion-joint system and belt are disclosed in U.S. pat. 5,228,255 to Hahn et al.
It should be understood that the terms "last stage" and "turbine wall", as used herein, include walls attached to the turbine for channeling steam from the turbine. Similarly, the term "condenser hood" includes walls attached to the condenser hood for channeling steam.
Another such expansion-joint system, with belt, is disclosed in U.S. patent application Ser. No. 08/701,330 filed on Aug. 23, 1996 by Robert B. Hahn et al.
These prior-art expansion-joints for use with steam turbines and condensers have normally employed expansion-joint belts of a type depicted generally in FIG. 2 herewith as belt 24 (although the particular version of this type belt depicted in FIG. 2 is a relatively new S-shaped belt, most such prior-art belts being straight in cross section as shown in U.S. Pat. No. 5,228,255 to Hahn et al.). Such prior-art belts have sometimes been referred to as dog-bone belts because they have included a relatively thin elongated web 26 (when viewed in cross-section) with knobs 28 at opposite ends, thereby somewhat resembling a dog-bone. Older versions of these dog-bone belts have included knob cores formed of cords, sometimes of an elastomer, positioned approximately at centers of the knobs 28 (not shown in FIG. 2, but see U.S. Pat. No. 5,288,255 to Hahn et al.).
Each of the last-stage belt clamping mechanisms 20 and the condenser belt clamping mechanisms 22, of these prior-art expansion-joint systems, has an expansion-joint clamping element 30, 32, attached directly or indirectly to a wall of the last stage 14 or the hood 12, and a clamping bar 34, 36, attached to the respective expansion-joint clamping element 30, 32 by bolts 38.
As can be seen in FIG. 2, in such prior-art systems both the expansion-joint clamping elements 30 and 32 and the bars 34 and 36 are machined to have grooves 40 and 42 which generally correspond in shape and size to the shape and size of the knobs 28. Thus, when the clamping bars 34 and 36 are tightly attached to their respective expansion-joint clamping elements 30 and 32, with the respective knobs 28 of the belt 24 in them, they squeeze the knobs 28 between them in their grooves, thereby creating seals between the clamping mechanisms 20 and 22, and the belt 24.
Although these prior-art systems have functioned relatively well, there are a number of problems associated with them. One problem is that it is difficult and expensive to manufacture such a large resilient belt and metallic clamping mechanism with sufficiently exact tolerances that a reliable mechanical seal is created. For this reason, it has even been suggested to provide Zrik fittings on the clamping bars 34 and 36 so that a sealant material can be injected under pressure into cavities formed by the clamping mechanisms 20 and 22 (see U.S. Pat. No. 5,228,255 to Hahn et al.).
A related problem is that it is costly to machine the necessarily accurate grooves 40 and 42 in the clamping elements 30 and 32, and the clamping bars 34 and 36
Yet another related problem is that in these prior-art systems the clamping bars 36 are unduly heavy and therefore difficult to handle. In this respect, because the clamping bars 36 must be machined to create the grooves 42, it is necessary to make them rather thick (11/4 inch) so that they have the necessary strength.
Although the clamping elements 30 and 32 are continuous about mouths of the hood 12 and the last stage 14, the clamping bars 34 and 36 are formed in clamping-bar segments 46 which have breaks 44 (which are exaggerated in FIG. 1 for clarity) between them, as is depicted generally in FIG. 1. The clamping bar segments are usually attached on the steam side of the turbine wall and condenser hood. These clamping-bar segments 46 are made in lengths which can be easily handled by an mechanic. If the linear weight of the clamping-bar segments 46 is unduly great, the clamping-bar segments must be made to have shorter lengths and more clamping-bar segments must be used. An increased number of clamping-bar segments 46 increases costs in manufacturing and installing. Also, an increased number of clamping-bar segments 46 increases the number of gaps 44, which, in turn, detracts from a seal created by the expansion-joint system 16.
It is an object of this invention to provide an expansion-joint system having a belt and hardware which is relatively easy and inexpensive to manufacture, but yet which provides a reliable seal with clamping mechanisms
It is a further object of this invention to provide an expansion-joint system having clamping mechanisms which are relatively inexpensive to manufacture and easy to use, yet which reliably hold knobs of the belt.